1. Technical Field
The present invention relates to a color processing apparatus and computer readable medium for color processing.
2. Related Art
Color processing is needed in order to match color spaces depending on different input/output devices. For example, image forming apparatuses, such as printers or electrophotographic apparatuses, use four or more color materials. Therefore, a color space using the colors of the color materials as elements is used as a device-dependent color space. In addition, display devices, such as monitors, and image reading apparatuses, such as cameras or scanners, use, for example, an RGB color space. In order to match the device-dependent color spaces, a perceptually uniform color space that does not depend on devices, such as CIELAB, or a color space having the characteristics of a color appearance model, such as CIECAM02, is used. In addition, for example, a tristimulus value CIEXYZ or an LMS color space is used.
The correction of a white point is one of the processes of combining the colors of different color spaces. In the display of an image by a display device or a reflected image using a paper medium, the white point (substantially corresponding to a point with the highest lightness) is not set at a given value, but is likely to vary depending on the processing system or the medium (for example, a sheet). Therefore, the white point needs to be corrected in order to match the dynamic ranges of given color information and color information to be output. In this case, the color space of the given color information may be converted into a common color space and a process of correcting the white point may be performed to convert the color space into a color space to which the processed color information will be output. In this way, the process of correcting the white point may be performed in the common color space. For example, the common color space may be CIELAB and the process of correcting the white point may be a process of correcting the color information of the CIELAB color space to the color information of the CIELAB color space.
As the correction of the white point, for example, there is a method that normalizes the white point using CIEXYZ, which is the colorimetric value of a white point of a sheet set by the specifications (IS015076-1) of an ICC profile (a method of normalizing relative colorimetric rendering intent uses a white point of a sheet instead of a light source that is used for conversion from the tristimulus value CIEXYZ to CIELAB. For example, since this processing method is implemented by conversion from CIELAB to CIEXYZ and color conversion from CIELAB to CIELAB that is performed during conversion from CIEXYZ to CIELAB, it is unclear whether the processing method is a CIEXYZ process or a CIELAB process. However, in principle, the processing method is equivalent to a structure that performs reversible connection using conversion into CIEXYZ, thereby omitting calculation. Therefore, in the invention, the processing method is represented as a conversion process from CIEXYZ to CIEXYZ).